1. Field of the Invention
The present invention relates to testing machines for printed circuit boards, and more particularly to fixtures of testing machines for expansion cards.
2. Description of the Related Art
As the computer industry matures, users have come to increasingly demand more powerful and more stable computers. In a typical computer, a plurality of expansion cards is assembled to expansion slot connectors of a motherboard in the computer, for making the computer more powerful. However, computer manufacturers must ensure that the expansion slot connectors in the motherboard are fully functional before releasing the computers into the marketplace. Therefore, a testing machine is needed to test the motherboard""s expansion slot connectors. A plurality of testing circuitries is provided in the testing machine for performing such a test.
To test the expansion slot connectors of a motherboard, an operator firstly inserts test cards into the expansion slot connectors of the motherboard one by one, and then actuates the testing machine to test the expansion slot connectors of the motherboard. After the testing machine has finished testing, the operator pulls the test cards from the expansion slot connectors one by one. However, such manual operation is slow, laborious and inefficient. Furthermore, manual operation may damage the test cards and the motherboard, due to inappropriate inserting and/or pulling force being applied. If the operator is inadvertent, the test cards may not be not properly matched with the respective expansion slot connectors, in which case the testing machine will give false results.
To address these problems of manual operation, a number of fixtures for test cards have been devised. Taiwan Patent No. 452087 discloses a fixture for test cards. The fixture comprises a movable board, a fixing base, a pair of bolts, a pair of coil springs, and a correcting plate. The fixing base defines a slot therein. The movable board defines an opening, corresponding to the slot of the fixing base. A longitudinal widened aperture is defined in a bottom of the correcting plate, corresponding to an expansion slot connector of a motherboard to be tested. A longitudinal narrowed hole is defined in a top of the correcting plate, in communication with the aperture. The fixing base is fixed on the movable board. The bolts are extended through the movable board near opposite ends of the fixing base and through the coil springs under the movable board, and are fixedly fastened with the correcting plate. A test card is fastened to the fixing base, and is extended through the slot of the fixing base and the opening of the movable board. In use, the movable board moves toward the motherboard until the aperture of the correcting plate contacts and receives the expansion slot connector therein. The movable board continues moving downwardly, the coil springs are compressed, the correcting plate is blocked by the expansion slot, and the bolts are pushed beyond the movable plate by the blocked correcting plate. The test card is then extended through the hole and the aperture of the correcting plate, and engages in the expansion slot connector.
However, the above fixture does not solve the above-described problem of potential inaccuracy of the test results. The basic requirement for accurate testing is that the movable board, the fixing board, the test card and the correcting plate are properly assembled. This ensures that the extension of the test card through the correcting plate is accurate. However, an overall tolerance of the fixture is liable to change over time, because the fixture sustains repeated impact when used again and again. It is also important that the motherboard is accurately positioned relative to the correcting plate. This ensures that the expansion slot connector of the motherboard is accurately received in the aperture of the correcting plate. However, in practice, it is very difficult to ensure accurate position of the motherboard relative to the correcting plate. When the fixture""s tolerance is changed and the motherboard is not accurately positioned, the test card is very prone to be incorrectly engaged in the expansion slot connector of the motherboard. In such case, the test results cannot be relied upon.
Accordingly, an object of the present invention is to provide a fixture which has an adjusting mechanism for accurately engaging a test card in an expansion slot connector.
Another object of the present invention is to provide a fixture which improves accuracy and reliability of tests performed on expansion slot connectors.
A further object of the present invention is to provide a testing machine incorporating a fixture which has a self-adjusting mechanism.
To achieve the above objects, a fixture in accordance with the present invention comprises an actuator, a self-adjusting unit, and a testing unit. The fixture is received in a testing machine. The self-adjusting unit comprises a first connecting plate and a second connecting plate. The first connecting plate is attached to the actuator. A first through hole is defined in each corner of the first connecting plate. The first through hole comprises a threaded portion and a stepped portion. The stepped portion of the first through hole defines a shoulder therearound. A second through hole is defined in each corner of the second connecting plate, corresponding to the first through hole. The second through hole comprises a shoulder portion, and a tapered portion. The shoulder portion defines a shoulder therearound. A plurality of coil springs is received in the stepped portions of the first through holes and the shoulder portions of the second through holes respectively. Opposite ends of each of the coil springs resiliently abut a corresponding shoulder of the first connecting plate and a corresponding shoulder of the second connecting plate respectively. A plurality of bolts extends through the second through holes of the second connecting plate, and engages in the threaded portions of the first connecting plate respectively. Each of the bolts comprises a head portion, a rod portion, and a threaded end portion. The head portion comprises a tapered surface, corresponding to the tapered portion of a corresponding second through hole of the second connecting plate. The tapered head portion is movably received in the tapered portion of the corresponding second through hole, with the threaded end portion engaging in the threaded portion of a corresponding first through hole. The testing unit is attached to the second connecting plate, and adapted for receiving test cards.
Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with the attached drawings, in which: